Wetlands - Nature's 'Horizontal Levees' - Blunt Storm Damage

Fish lived then on the west side of Old Saybrook close to the Long Island Sound shoreline. As Donna's 100-mph winds swept through southeastern Connecticut, he recalled, the Great Hammock tidal marsh between his neighborhood and the Sound filled quickly with waters from the storm surge. Some roads in the neighborhood flooded, but homes and other property were for the most part spared.

At that moment his appreciation for tidal marshes deepened, as he saw firsthand how these wet grasslands at the shoreline can act like giant sponges that absorb the surge. Had the marsh been filled in for development or otherwise degraded - a fate about 30 percent of Connecticut's marshes fell to before laws protecting tidal wetlands took effect in 1970 - his neighborhood would surely have had more damage. Characterized by porous soils and regular flushing by tides and fresh water, salt and brackish marshes were once considered wastelands but now are valued as critical habitat for wildlife, pollution and sediment filters and buffers against flooding.

”It's always been one of the reasons for protecting marshes,” said Fish, who is now chairman of the Old Saybrook Conservation Commission. “We knew marshes were important for that reason.”

During the 1938 hurricane, which occurred 70 years ago Sunday, Great Hammock Marsh also absorbed significant storm surge - along with some cottages uprooted from a nearby barrier beach.

Before-and-after historical aerial photographs of the area show cottages on an exposed barrier beach seaward of the marsh carried onto the wetlands with the storm, noted Ron Rozsa, coastal ecologist for the state Department of Environmental Protection. In Connecticut, he said, most tidal wetlands sit between the uplands and a barrier beach, not right on the shoreline.

”Barrier beaches in Connecticut take the brunt of hurricane impact,” said Rozsa, “but we recognize that marshes also play some role in dampening the surge.”

A new study quantifies just how much protection these wetlands provide.

In an article published in June, University of Vermont ecological economics professor Robert Costanza and other researchers report that their analysis of hurricane strength, property damage, property values in vulnerable coastal areas, wetland acreage and other factors shows that wetlands prevent an estimated $23 billion in annual damage from hurricane winds and flooding in the Northeast and Gulf Coast. The analysis looked at 34 hurricanes from 1980 to 2004.

In Connecticut, which gets hit by a major hurricane on average once every 10 years, every 2.5 acres of coastal wetlands can be credited with preventing about $28,500 in storm damage each year, according to the study. It considered a little more than half of Connecticut's 22,000 acres of coastal wetlands to be in the zone directly affected by hurricanes.

”They have value as places to absorb floodwaters that would otherwise accumulate elsewhere,” Costanza said in a telephone interview. “The more wetlands a state has, the better off it's going to be for storm damage.”

His study calls tidal wetlands “horizontal levees” maintained by nature that are more economical and effective at damage prevention than man-made vertical levees. They absorb storm energy, slow incoming waves and winds and pool surge waters. This is in addition to the other significant ecological, aesthetic and recreational values of wetlands. Restoring, protecting, and, when possible, expanding tidal wetlands, Costanza argues, is a highly cost-effective protection strategy for hurricane-prone areas.

”By quantifying the value of these services, it gets people's attention,” Costanza said. “We need to work with natural forces, not try to overpower them.”

Connecticut restores wetlands

Thirty years ago, Connecticut began a tidal wetlands restoration program that has brought back about 1,750 acres of degraded marshes by returning natural tidal flows blocked by dikes, plugging ditches dug to drain or pool water and excavating fill.

”At this point,” said Rozsa, “we're running out of projects, because we've been at this for 30 years. What's left are the really difficult or expensive or impossible projects.” Some of these would require moving houses.

Still, with rising sea levels and a predicted increase in the frequency and intensity of hurricanes from climate change, tidal wetlands could become even more important as hurricane buffers, the study points out, so that making investments to expand and preserve them are warranted.

”If we lose them, it will cost a lot more to replace them,” said Costanza, the lead author of the study.

Hurricane surge maps prepared by the U.S. Army Corps of Engineers point to some of southeastern Connecticut's most significant marshes.

Larger marshes in the most flood-prone areas with a greater potential to protect adjacent developed areas against flooding include the Great Island and Upper Island complex at the mouth of the Connecticut River in Old Lyme, the Pattagansett marsh between Black Point and Giant's Neck in Niantic, the Barn Island marshes in Stonington and the marshes at Waterford Town Beach and Alewife Cove.

Statewide, about 30 percent of the coastal marshes are state-owned, while groups like the Nature Conservancy and private owners claim others. But the law enacted in 1970, Rozsa said, basically prohibits any activity that would impact them.

”The tidal wetlands act has a preservation-oriented policy,” he said, “so for all practical purposes, they are all protected.”